Composite pipe, process for producing the same, and heat pipe using the same

ABSTRACT

A composite pipe is proposed which is comprised of an aluminum pipe and a lead pipe formed in the aluminum pipe in direct contact with the inner wall of the aluminum pipe. The composite pipe is produced by supplying a lead pipe to a continuous aluminum extrusion machine which can extrude while enveloping a long object, to form an aluminum pipe on the outer periphery of the lead pipe. A heat pipe using the composite pipe is also proposed.

This is a division of U.S. patent application Ser. No. 064,390 filedJune 22, 1987, now U.S. Pat. No. 4,817,259, granted Apr. 4, 1989 whichis a division of Ser. No. 811,164 filed Dec. 19, 1985 now U.S. Pat. No.4,733,699 granted Mar. 29, 1988.

The present invention relates to a composite pipe, process for producingthe same, and a heat pipe using the same.

Alminum is high in electric conductivity, non-magnetic, high in heatconduction, and light in weight, and also has excellent ductility andmalleability, and easy for continuous extrusion. It has recently beenused e.g. as a metal sheath of long electric power cables for the sakeof these advantages.

Aluminum pipes are continuously extruded by means of a continuousextrusion machine which can extrude while enveloping a long object.Thus, long seamless pipes can be produced. Besides, since the materialitself is soft, pipes of a small diameter are flexible withoutcorrugation, and can be transported by winding around a drum. Also, thepipes of a large diameter can be easily corrugated, and can be easilywound around a drum or laid at winding places. Furthermore, aconsiderable maximum tensile stress can be expected for aluminum, thoughnot as high as that of iron, and it is possible to obtain pipes whichcan withstand a considerably high internal pressure.

However, aluminum pipes are inferior in corrosion resistance withoutparticular anticorrosive treatment can be easily attacked by water,steam or methanol, and the abovesaid advantages can not be fullyexhibited. For instance, aluminum pipes are not generally used fortransportation of water, steam or chemical solutions such as methanol.If aluminum pipes are used for heat pipes with water or methanol used asthe working fluid because of their high heat conduction, low price andsafety, hydrogen gas may be generated due to reaction between thisworking fluid and aluminum after lapse of a long time. Thus, the workingfluid is limited to Freon or the like.

On the other hand, lead is a very stable metal against corrosion, andresists water, steam and many chemicals. Lead is also high inconductivity, non-magnetic, high in heat conduction, rich in ductility,malleability and flexibility, and is applicable to long extrusionprocess. To the contrary, it is too soft and is poor in maximum tensilestress, which means that it cannot be used at high pressure whenproduced into pipes. Besides, it is very heavy. Hence, when it is usedas pipes, its use has been extremely limited.

An object of the present invention is to provide corrosion resistantlong composite pipes having both the advantage of lead and that ofaluminum.

Another object of the present invention is to provide a process forproducing such composite pipes.

A further object of the present invention is to provide a heat pipe withwhich water and methanol can be used as working fluid by using thecomposite pipe.

The term "a continuous extrusion machine which can extrude whileenveloping a long object" means, in the case of alminum; e.g. analuminum press for metal extrusion of power cable manufactured byHydraulik GmbH of Germany and an aluminum press manufactured bySchloemann GmbH of Germany, and in the case of lead, means e.g. aso-called vertical lead encasing machine and a screw extrusion typemachine widely used to produce a metal sheath of power cable, generallyknown as the Hansson type lead encasing machine.

In accordance with the present invention, there is provided a compositepipe comprising an aluminum pipe and a lead pipe, the latter being incontact with the inner wall of the aluminum pipe either directly orthrough a protective layer.

Since the lead pipe provided inside is resistant to corrosion by water,steam chemical such as methanol, or gas is used inside, such compositepipes have excellent corrosion resistance. Since a lead pipe is soft andsmall in maximum tensile stress, its form retaining ability is inferiorand the internal pressure of the pipe cannot be raised. But theseshortcomings resulting from its softness are compensated for by thealuminum pipe at outside. So, good pressure resistance and flexibilityare obtained on the entire composite pipe. Thus, a long, seamless,flexible, and highly pressure-proof pipe is obtained which can transportliquids such as water and chemicals, and gas such as steam.

In accordance with the present invention, the composite pipe ismanufactured as described below. After manufacturing a long lead pipe byuse of a continuous lead extrusion machine, the lead pipe is suppliedinto a continuous lead extrusion machine, the lead pipe is supplied intoa continuous aluminum extrusion machine which can extrude whilecontinuously enveloping a long object, such as a metal sheath extruderfor power cable, to coat the lead pipe with an aluminum pipe on itsoutside.

This may be performed by firstly winding a heat-soluble synthetic resintape around the lead pipe to form a shape retaining layer and supplyingthe lead pipe to the aluminum extruder to form an aluminum pipe on thelead pipe while applying a sufficient pressure to the inside of the leadpipe to expand it when the shape retaining force of the shape retaininglayer has decreased by heat. With this process, the tape of the shaperetaining layer on the lead pipe melts in the extruder, allowing thelead pipe to expand under the internal pressure. On the lead pipe whichis expanding, an aluminum pipe is formed by the extruder without any gapwith respect to the lead pipe. If heat in the extruder is insufficientto melt the tape, a separate heating means may be used.

Or alternatively, after manufacturing a long lead pipe by use of acontinuous extrusion machine, the lead pipe may be supplied into analuminum continuous extrusion machine which can extrude whilecontinuously enveloping a long object, to form an aluminum pipe on thelead pipe and pressure medium is sealed into the lead pipe to expand thelead pipe, so that the lead pipe will be expanded and pressed againstthe inner wall of the aluminum pipe more tightly.

In this case, the lead pipe may be brought into contact with the innerwall of the aluminum pipe directly or through a protective layer such aspaint, adhesive cloth tape, heat-fusion plastic tape or extruded plasticlayer.

By such a method, a composite pipe having a lead pipe placed in contactwith the inner wall of an aluminum pipe can be obtained.

The heat pipe according to this invention has a container, which is acomposite pipe comprising an aluminum pipe and a lead pipe mounted incontact with the inner wall of the aluminum pipe and working fluidcharged into this container. A wick material is put into the containerif necessary.

Therefore, since the working fluid is in contact with the corrosionresistant lead pipe, either water or methanol may be used as workingfluid. What is more, since both metals are excellent in heat conduction,either the heat absorbing part or the heat discharging part of the heatpipe does not show a particularly high heat resistance.

Other features and objects of the present invention will become apparentfrom the following description taken with reference to the accompanyingdrawings, in which:

FIGS. 1-4 are sectional views of the composite pipes embodying thepresent invention;

FIGS. 5-10 are schematic views showing how the composite pipes areproduced;

FIG. 11 is a perspective view of a dies;

FIG. 12 is a schematic view of a heat pipe embodying the presentinvention; and

FIGS. 13-16 are sectional views showing how the composite pipes of thepresent invention are connected.

A composite pipe 1 according to this invention comprises an aluminumpipe 2 and a lead pipe 3 disposed in the aluminum pipe in contact withthe inner wall of the aluminum pipe.

As the material for the lead pipe 3, lead or lead alloy (Cu+Te alloy, Calloy, 1/2 C alloy, etc.) applicable to the continuous extrusion processmay be used.

On the outer surface of the aluminum pipe, as shown in FIG. 2, aprotective layer 4 of polyethylene, polyvinyl chloride, polybutene,nylon or the like may be formed by extrusion to improve the corrosionresistance of the outer surface of the aluminum pipe or to serve as aheat insulating layer. The protective layer 4 may be composed of asingle or plural plies of tape of fusible polyethylene or rubber linedcloth. Or, for a greater efficiency of heat exchange on the outersurface of aluminum pipe 2, if the adiabatic protective layer is notprovided on the aluminum pipe, if the external surface of the aluminumpipe may contact a corrosive gas, such as SO₂ and SO₃, or water,chemicals or other liquids or steam, a protective layer 4 of lead pipeshould be formed on the outside of the aluminum pipe 2 for the samereason the outside of the aluminum pipe 2 for the same reason of placinga lead pipe 3 on the inner wall of the aluminum pipe 2. If theprotective layer 4 is made of lead or lead alloy, the thermal conductionbetween inside and outside the composite pipe is particularly excellentas mentioned above. Furthermore, where heat insulation is required, theprotective layer 4 should preferably be composed of a foamed plasticsuch as foamed styrol or foamed polyethylene, or glass wool or absestos.In this case, as shown in FIG. 3, a second protective layer 12 should bepreferably formed on the protective layer 4 to retain the shape, preventdamage, resist water and corrosion and insulate heat. The layer 12 maybe formed by extrusion of polyethylene, polyvinyl chloride, polybuteneor nylon, or by winding a tape of fusible polyethylene or rubber linedcloth.

The composite pipe 1 according to the present invention may bemanufactured in the following manner.

Firstly, a lead pipe 3 is extruded by use of a continuous lead extruder5. The lead pipe is then supplied into a continuous aluminum extruder 6which can extrude while enveloping a long object and, using the leadpipe 3 as a core, aluminum is continuously spread on the outer surfaceof lead pipe 3 to form an aluminum pipe 2 on the lead pipe.

The aluminum pipe 2 may be formed while expanding the lead pipe, in themanner described below. Before supplying a lead pipe to the continousaluminum extruder 6, a heat-soluble tape of synthetic resin is tightlywound around the lead pipe to form a shape retaining layer. The leadpipe is then supplied to the extruder while applying pressure to theinside of the lead pipe e.g. by gas. The pressure applied into the leadpipe should be such that at normal temperature the shape retaining layerformed on the outer surface of the lead pipe will prevent the lead pipefrom expanding and the lead pipe will expand easily at temperatureswhere the synthetic resin tape forming the shape retaining layer meltsor softens.

When the lead pipe is supplied to the extruder 6, the synthetic resintape will melt by heat in the extruder and the shape retaining force ofthe shape retaining layer will decrease, so that the lead pipe 3 willexpand by the internal pressure. Aluminum will be spread on the expandedlead pipe so that an aluminum pipe 2 will be formed on the outer surfaceof the lead pipe 3.

Because the lead pipe not coated with aluminum has a poor strength, itis often flattened when it is wound around a drum after extrusion. Ifthe flattened lead pipe were supplied to the aluminum extruder 6 as itis, it might clog the point of the extruder. With the abovementionedprocess, if it is flattened when wound around a drum, it will becorrected so as to be circular because it is expanded by the internalpressure. This prevents the lead pipe from clogging the extruder.Therefore, it is unnecessary to have the diameter of the point ofextruder much larger than that of the lead pipe 3. Thus, it is possibleto form a lead pipe of a diameter slightly smaller than that of thealuminum pipe inside of the aluminum pipe 2. This decreases the degreeof expanding the lead pipe after forming an aluminum pipe on the leadpipe, thus decreasing the degree of impairing the strength of the leadpipe by expansion. Higher production speed is another advantage. Afurther advantage is that even if the lead pipe is thin, the roundnessof the lead pipe can be extremely high. Thus, composite pipes can beproduced with high reliability and high productivity.

The shape retaining layer also serves as a mar preventive layer. Thesynthetic resin tape for the shape retainig layer may be made ofpolyethylene, vinyl chloride, polybutene or other material which meltsat a temperature of 100° to 150° C.

The abovementioned process is also applicable to cases in which on thelead pipe is formed not an aluminum pipe but a welded corrugated pipe ofsteel, copper or stainless steel, or a plastic pipe such aspolyethylene, vinyl chloride, polybutene or nylon.

If electric corrosion due to direct contact between different metals isfeared, it is preferable to place a protective layer between the leadpipe 3 and the aluminum pipe 2. For this purpose, cloth tape, plastictape or the like may be wound, either directly or together with anadhesive, paint or the like, on the continuously extruded lead pipe 3after it has left the lead continuous extruder or in a separate process.A protective layer of polyethylene, polyvinyl chloride or the like maybe formed on the lead pipe 3 in a separate process by extrusion.

To improve the contact between the aluminum pipe 2 and the lead pipe 3,air should not be preferably present between the two pipes. For thispurpose, as shown in FIG. 5, a preferable process is to put a supplydrum 14 having a lead pipe 3 wound therearound into a vacuum supply tank13 known in the manufacture of OF (oil-filled) power cable, evacuate thesupply tank 13 by means of a vacuum pump 15, and feed the lead pipe to acontinuous aluminum extruder 6 in a vacuum state to coat the lead pipe 3with an aluminum pipe 2. In FIG. 5, numeral 16 denotes a drum for takingup the composite pipe 1.

Furthermore, to improve the contact between the aluminum pipe 2 and thelead pipe 3, an adhesive effective to adhere two metals without leavingair therebetween, such as formal, or tar or petroleum paint or othercorrosion preventive paint is filled in a dip tank 17 (FIG. 6), and thelead pipe 2 is sufficiently dipped in this tank and is then fed into thealuminum extruder 6 to obtain the composite pipe 1. In this case, thoughnot shown in the drawing, an adhesive layer is formed between the leadpipes and the aluminum pipe 2 of the composite pipe 1 of FIG. 1.

In this process, if this composite pipe 1 is used as the container of aheat pipe, a wick material 7 may be fixed to the inside of the lead pipe2 of the composite pipe 1 in the following manner. If carbon fiber ormetal mesh is used as the wick, in order to retain the shape of the wickmaterial 7, a spiral 8 may be formed (FIG. 7) by use of stainless steel,copper, nylon or FRP. The wick material 7 is wound around the spiral 8,and fixed thereto by a binder material 9 (cloth tape, metal tape, wire,etc.), if necessary. The wick material 7 fixed to the spiral 8 is thensupplied into a continuous lead extruder 6 which can extrude whileenveloping a long object and, using the wick material 7 as the core,lead is continuously spread on the wick material 7 to form a lead pipe3. (FIG. 8). The lead pipe thus formed may be cut to suitable lengths orwound around a drum, as required. The lead pipe is then supplied into acontinuous aluminum extruder 6 which can extrude while enveloping a longobject (FIG. 9). Aluminum is continuously spread on the lead pipe 3which is used as the core, to form an aluminum pipe 2. The details ofthis manufacturing process are the same as in the production of theabovesaid composite pipe 1. In this state, in the case of alarge-diameter pipe, it may be corrugated, if necessary, to improve theflexibility, by means of a corrugating machine. The composite pipe 1thus manufactured may be cut to required lengths or wound around a drum.

In the above process, since the inside diameter of the aluminum pipe 2manufactured by extrusion molding can be controlled very precisely, gapis seldom formed between the lead pipe 3 and the aluminum pipe 2. Whencorrugated as mentioned above, the aluminum pipe usually shrinks indiameter and bites into the lead pipe 3, so that the contacttherebetween is further improved.

However, if the lead pipe 3 is partly hollowed or deformed due tocorrugation to cause some gap between the lead pipe 3 and the aluminumpipe 2, both ends of the lead pipe 3 are fully closed and pressuremedium such as gas and liquid should be sealed therein to pressurize thelead pipe against the inner wall of the aluminum pipe 2 (e.g. 2 to 50kg/cm²), thereby reforming the lead pipe to improve the contact betweenthe alumunum pipe and lead pipe. As the method for contacting the leadpipe, it is sufficient to pressurize the lead pipe in the atmosphere atordinary temperature. But, in order to pressurize more efficiently andsecurely, as it will be explained later, the composite pipe may be putinto a supply tank 13 for power cable shown in FIG. 5, wound around adrum, and, though it is not necessary to evacuate the tank 13, theinside of the tank 13 be heated to 100° to 250° C. by passing steamthrough the steam coil provided in the tank 13, and the lead pipe 3 bepressurized in this state.

In the case of an extremely short composite pipes or composite pipehaving a wick, the lead pipe may be brought into closer contact with thealuminum pipe by manufacturing the lead pipe and aluminum pipeseparately, inserting the lead pipe into the aluminum pipe 2, puttingthe lead pipe into the tank 13 with its both ends ready to be fullyclosed, heating and evacuating the tank 13 to heat and pressurize thelead pipe while removing air from the gap between the lead pipe 3 andaluminum pipe 2 to cause the lead pipe 3 to contact the aluminum pipetightly.

In this case, the heating temperature is not more than 250° C. becausethe strength of the aluminum pipe is lowered at higher temperature andalso the strength of the lead pipe drops significantly, so that locallyweak parts may be damaged by the internal pressure. For expansion of thelead pipe 3, the maximum limit of internal pressure should be 50 kg/cm²,because with the composite pipe of a large diameter, not only the leadpipe but also the aluminum pipe may be deformed at higher pressure. Asthe method of pressurization, if the maximum pressure is appliedsuddenly, locally weak parts of the lead pipe 3 may be broken. So it ispreferable to raise the pressure gradually, for example, by holding 5kg/cm² for an hour, 10 kg/cm² for an hour, 15 kg/cm² for an hour, and soforth until reaching the maximum pressure.

As shown in FIG. 4, the outer surface of the aluminum pipe 2 may be, forprotection from corrosion and heat insulation, coated with rustpreventive paint 29 and then polyethylene or polyvinyl chloride 10.Furthermore, an insulating material 11 such as asbestos and glass woolmay be wound around the outer surface. Or, as shown in FIG. 3, a secondprotective layer 12 may be formed on the protective layer 4.

Thus, a composite pipe 1 for heat pipe is produced having such a sectionas shown in FIG. 4, if the wick is needed, or in FIG. 2 or FIG. 3 if nowick is needed.

Depending on the application, if the outer surface of the aluminum pipe2 cannot be coated with a nonmetallic paint, as shown in FIG. 2, it ispreferable to coat the outer surface of aluminum pipe 2 with a copperpipe as a protective layer 4 by means of a continuous lead extruder 5which can extrude while enveloping a long object in the procedure shownin FIG. 8. To improve the contact between the protective layer 4 and thealuminum pipe 2, after extrusion molding, it is preferable to subjectthe pipe to draw or press forming by use of dies or rolls.

Next, as shown in FIG. 10, by inserting a lead pipe 3 into an aluminumpipe 2 and expanding the lead pipe by sealing a pressure medium in it,the lead pipe may be brought in tight contact with the inner wall of thealuminum pipe.

In doing so, if the wall thickness of the lead pipe 3 is relativelysmall and its length is relatively short, an aluminum pipe 2 slightlylarger in diameter than a lead pipe 3 may be manufactured beforehand byan unspecified aluminum pipe extruder, and a lead pipe 3 manufactured byextrusion molding may be inserted into the aluminum pipe 2 right afterextrusion. The both ends of the lead pipe 3 are closed and a pressuremedium is charged thereinto to expand the diameter of the lead pipe,thereby causing the lead pipe to contact tightly the inner wall of thealuminum pipe. At this time, with an end of the lead pipe 3 closed, thelead pipe may be extruded and inserted into the aluminum pipe 2 whilepressurizing to such an extent as to retain the shape by air or the likefrom the extrusion outlet of the continuous lead extruder 5. If a leadpipe having a sufficient wall thickness to retain its shape atatmospheric pressure is used, a lead pipe and an aluminum pipe may beseparately prepared, and the lead pipe may be inserted into the aluminumpipe.

When manufacturing a pipe long enough to be wound around a drum, thefollowing procedure is applicable. Firstly, a lead pipe having asufficient wall thickness to retain its shape and having as large adiameter as possible but insertable into an aluminum pipe of a desireddiameter is prepared. The lead pipe is supplied into a continuousaluminum extruder which can extrude while enveloping a long object toform an aluminum pipe 2 on the outer surface of the lead pipe as shownin FIG. 10. Next, a pressure medium of gas or liquid is sealed in thelead pipe 3, and the lead pipe is pressurized gradually toward theoutside (e.g. initially 2 to 5 kg/m² G) to expand the diameter of thelead pipe 3 gradually to contact it against the inner wall of thealuminum pipe 2. In this case, it is preferable to pressurize the leadpipe while evacuating the gap between the lead pipe and the aluminumpipe by means of a vacuum pump. At this time, the aluminum pipe 2 andlead pipe 3 may be put in a vacuum drying tank used in the manufactureof ordinary OF power cable, wound around the drum, and while heating to100° to 200° C. the aluminum pipe 2 and the lead pipe 3 are evacuatedeither together with the tank with both ends of a gap (a in FIG. 10)formed between the aluminum pipe and the lead pipe being kept open, orwith both ends of the gap closed when the tank is at atmosphericpressure, so that the lead pipe 3 will be tightly contacted with theinner wall of the aluminum pipe 2.

The method of pressurizing the lead pipe 3 and evacuating the gapbetween the lead pipe and the aluminum pipe will be further describedbelow. Both ends of the aluminum pipe and the lead pipe are closedtightly, if necessary, by use of terminating metals and both closed endsare reinforced with expoxy or the lime, and branch pipes are provided tocommunicate with the gap a and the inside of lead pipe, and the branchpipe communicating with the gap a is used in evacuating, while thebranch pipe communicating with the inside of lead pipe 3 is used inpressurizing.

In this process, if the lead pipe does not have a spiral 8 for retainingits shape or a sufficient wall thickness to retain its shape, it may besupplied into a continuous aluminum extruder while retaining its shapeby means of dies 18 of a half split type made of wood block or nylon asshown in FIG. 11.

When using a composite pipe 1 manufactured in the abovesaid process as aheat pipe, working fluid may be sealed merely with both ends closed, ifwick is not needed. If needed, after the inside of the lead pipe hasbeen lined with wick material 7, working fluid may be sealed. In thecase of a long heat pipe, if the required length is known, the pipe maybe charged with working fluid in a factory. If the required length isnot known, the composite pipe 1 lined with wick material 7 may be laidfrom a drum reel, be evacuated from its one or both ends, and be chargedwith a required volume of working fluid. Now, a heat pipe is obtained byclosing its both ends. If a heat pipe is manufactured in this way, itmay be easily suited to the actual field laying conditions. Thus apractical heat pipe may be obtained.

FIG. 12 shows an example of the heat pipe in use on which a heatinsulating part 19 is formed by providing a heat insulation andprotective layer in the center, with a heat absorbing part 20 and a heatreleasing part 21 formed at both ends. If both parts A and B surroundingthe heat absorbing part 20 and the heat releasing part 21 are both air,the insulation layer and protective layer are peeled off at both partsto expose the aluminum pipe 2. Fins 22 may be provided on the parts, ifnecessary. If part A is steam or hot water and part B is air, a leadpipe must be spread on the outside of the aluminum pipe at least part A.However, it is not necessarily required to apply a lead pipe over theentire length. At least the metal surface of the heat absorbing part 20in contact with part A has to be encased. Of course, the aluminum pipe 2may be protected not with a lead pipe but with a corrosion preventivematerial such as thin Teflon, although this decreases the efficiency ofheat exchange. As for part B, if prevention of corrosion is necessaryfor the aluminum pipe, the same treatment as in part A may be applied.

Next, it will be described how the composite pipes according to thepresent invention should be connected.

Firstly, the end of the aluminum pipe 2 at the end of the composite pipe1 is cut off to expose part of the lead pipe 3, as shown in FIG. 16A.The exposed portion 23 is then expanded (as in FIG. 16B) in a verticaldirection by use of a tube expander to form a flange. The tube expanderused should be made of e.g. nylon not to mar the inner wall of the leadpipe 3.

In the example of FIG. 13, the composite pipes 1 having a flange 23formed at their end in such a manner are connected by bringing togethertheir flange portions 23 with a packing 24 therebetween, mountingaluminum flanges 25 on the flanges 23, and tightening the flanges 25together with bolts. O-ring 26 of rubber may be placed between the edgeof the aluminum pipe and the expanded portion 23 of the lead pipe toprevent the outer wall of the lead pipe from being marred by the edge ofthe aluminum pipe.

In the second example of FIG. 14, the flange portions 23 are broughttogether with a packing 24 therebetween and fully caulked together.Glass tape impregnated with epoxy resin is then wound around theconnected portion to form a reinforced layer 27.

In the third example of FIG. 15 the exposed portion of one compositepipe 1 is not expanded whereas that of the other composite pipe isexpanded slightly. The expanded end 28 of the other pipe is put on theexposed but not expanded end of one pipe with a packing 24 therebetweenand they are fully caulked together. Glass tape impregnated with epoxyresin is wound around the connected portion to form a reinforced layer27.

With the abovementioned method for connection, flanges can be formedmerely by exposing part of the lead pipe and expanding the exposed end.Aluminum flanges or glass tape impregnated with epoxy resin are the onlynecessary parts. Therefore, the connection is possible with low cost andlight weight.

The composite pipe of this invention, which has a corrosion resistantlead pipe in contact with the inner wall of an aluminum pipe, can beused to convey water, steam, chemicals, or other liquids or gases, ortheir mixtures, which could not be conveyed by the aluminum pipe alone,while heat insulating where necessary.

Since the outside of the composite pipe is an aluminum pipe, a longseamless pipe can be manufactured by extrusion molding. The entirecomposite pipe is flexible enough to be carried wound around a drum orlaid at winding places. Thus, the reliability and ease of installationare outstandingly high as compared with the conventional installationmethod of a long pipe by connecting short pipes in the field by weldingor flange connection.

If heat insulation is required, the pipe may be treated with insulatingmaterial at shop. This suggests that the usefulness of this compositepipe is extremely high as compared with the conventional process ofapplying heat insulation treatment at least at the connected parts orover the entire length, if necessary, in the field, after connectingshort pipes together.

Furthermore, by the process of this invention, such excellent compositepipes can be manufactured easily.

Since the heat pipe of this invention is achieved by forming a compositepipe by mounting a lead pipe to the inside of an aluminum pipe, fittinga wick material, if necessary, to the inner wall of the lead pipe of thecomposite pipe, and sealing with working fluid, the kind of workingfluid is not limited. It can be used with water, methanol and otherswhich the conventional aluminum pipes could not use.

What we claim:
 1. A heat pipe having as a container a composite pipecomprising an aluminum pipe and a lead pipe provided in said aluminumpipe and having its outer wall in contact with the inner wall of saidaluminum pipe, and a working fluid sealed in said container.